38 



SOIL BACTERIOLOGY 



Exercise 4 

 Ammonification of Gelatin in Solution 



1. Prepare eight large Erlenmeyer flasks with 100 c.c. 

 each of gelatin solution (m. 17). 



2. Stopper loosely with cotton and sterilize in the auto- 

 clave at 15 pounds' pressure for ten minutes. 



3. Inoculate six of the flasks with 5 c.c. of a soil suspen- 

 sion. 



Note. — Shake 100 gm, of field soil with 200 c.c. of sterile water and allow 

 the coarse particles to settle. 



The two remaining flasks keep as controls. 



4. Incubate all of the flasks at 28° C. 



5. At intervals of two, four, and six days remove duplicate 

 flasks from the incubator and analyze the contents for 

 ammonia (see p. 141). At the time, of the last analysis 

 determine the ammonia in controls and subtract from the 

 total amount in the cultures. 



6. Tabulate results. 



Table 10. — Ammonification of Gelatin in Solution 



No. 



Time. 



Ammonia nitrogen in loo c.c. of 

 solution. 



Average. 



Nitroi^en 



Total. 



Blank 

 subtracted. 



ammonified. 



I 



2 



Days. 

 2 

 2 



Mgm. 



Mgm. 



Mgm. 



Per cent. 



3 

 4 



4 

 4 





» 







S 

 6 



7 

 7 











